algebra question

I need help with this problem, I'm unsure as whether to distribute the h or not.

Solve for "a"

D=1/5h(a-b)

As well as this...

An actor invests some money at 7%, and 47,000 more than four times the amount at 12% The total annual interest earned from the investment is 49640. How much did he invest in each amount?
He invested ___ at 7% and ___ at 12%

An actor invests some money at 7%, and 47,000 more than four times that amount at 12% The total annual interest earned from the investment is 49640. How much did he invest in each amount?
He invested ___ at 7% and ___ at 12%